1. Field of the Invention
The present invention relates to an adhesion type (contact type) area sensor having an image sensor function. In particular, the present invention relates to an adhesion type area sensor having an EL element as a light source and structured by a plurality of thin film transistors arranged in a matrix shape. The EL element called a light emitting element or a light emitting diode or an OLED (Organic Light Emission. Diode) includes triplet-based light emission element and/or singlet-based light emission element, for example. Further, the present invention relates to a display device combined with an adhesion type area sensor.
2. Description of the Related Art
Solid state imaging devices having a photoelectric conversion element such as a diode or a CCD for outputting an electric signal having image information from an optical signal having information such as characters and drawings on a page, and picture information have come to be used in recent years The solid state imaging devices are used in devices such as scanners and digital cameras.
There are line sensors and area sensors in solid state imaging devices having a photoelectric conversion element. A line sensor takes in an image as an electrical signal by scanning photoelectric conversion elements formed in a linear shape over a subject.
In contrast, an area sensor, also referred to as an adhesion type area sensor, has photoelectric conversion elements formed in a plane and arranged above a subject, and takes in an image as an electrical signal. It is not necessary to scan the photoelectric conversion elements with the area sensor, differing from the linear sensor, and therefore components such as a motor for scanning are unnecessary.
FIGS. 24A and 24B show a structure of a conventional area sensor. Shown in FIG. 24A is a perspective view of the area sensor, while a cross sectional diagram of the area sensor is shown in FIG. 24B. A sensor substrate 2501 on which a photoelectric conversion element is formed, a backlight 2502, and a light scattering plate 2503 are formed as shown in the figures.
Light from the backlight 2502 as a light source is refracted within the light scattering plate 2503, and is irradiated to a subject 2504. The irradiated light is reflected by the subject 2504, and is irradiated on a photoelectric conversion element formed on the sensor substrate 2501. An electric current of a size corresponding to the brightness of the light is generated within the photoelectric conversion element when the light is irradiated to the photoelectric conversion element, and image information from the subject 2504 is taken in as an electrical signal within the area sensor.
If the light from the backlight 2502 is not irradiated uniformly to the subject 2504 with the area sensor stated above, an irregularity develops in which the read in image becomes partially brighter and partially darker. It therefore becomes necessary to devise a structure of the light scattering plate 2503 is so that the light is irradiated uniformly to the subject 2504, and to precisely regulate the position of the backlight 2502, the light scattering plate 2503, the sensor substrate 2501, and the subject 2504.
Furthermore, suppression of the size of the backlight 2502 and the size of the light scattering plate 2503 is difficult, and therefore making the area sensor itself smaller, thinner and lighter is impeded.